Wideband Circularly Polarized Planar Antenna Array for 5G Millimeter-Wave Applications

A novel wideband circularly polarized (CP) planar array antenna is proposed in this article for the upcoming fifth-generation (5G) millimeter-wave (mm-wave) applications. The antenna element is fed by a slot etched on the substrate integrated waveguide (SIW) for convenient integration. It consists of two additional semicircle patches and two suspend metal posts which are working as the newly proposed polarizers for broadband CP operation. The combined patch, post, and slot generate totally four CP modes which greatly expand the antenna 3 dB axial ratio (AR) bandwidth. The antenna operating mechanism and the design procedure are illustrated in detail. The simulated results for the antenna element show an AR bandwidth of 41.28% from 25.66 to 39.01 GHz, an impedance bandwidth of wider than 44.62% from 24.41 to 38.43 GHz, and a gain of 7.25 +/- 1 dBic over the frequency band. The antenna shows a stable pattern and wide AR/impedance overlapping bandwidth (25.66-38.43 GHz), which covers most of the current 5G mm-wave bands. To enhance the antenna gain for practical application, a planar 4 x 4 antenna array fed by a fully incorporated SIW network is designed, fabricated, and measured. The measured results for the array demonstrate an AR bandwidth of 36.51% from 25.3 to 36.6 GHz, an impedance bandwidth of 40.21% from 24.42 to 36.71 GHz, and a peak gain of 19 dBic. The proposed antenna features a novel broadband CP working principle, low profile, and good radiation performance, which is well suited for 5G mm-wave applications.